Bees use their ability to “see” polarized light when foraging for food, researchers based at the University of Bristol have discovered. This is the first time bees have been found to use this ability for something other than navigation.
Like many other insect pollinators, bees find their way around by using a polarization-sensitive area in their eyes to “see” skylight polarization patterns. However, while other insects are known to use such sensitivity to identify appropriate habitats, locate suitable sites to lay their eggs, and to find food, a non-navigation function for polarization vision has never been identified in bees — until now.
Professor Julian Partridge and colleagues investigated whether bumble bees (Bombus terrestris) can learn the polarization patterns of artificial flowers in order to obtain a food reward.
They found that freely foraging bumble bees soon learned to differentiate between rewarding (sucrose solution providing) and aversive (quinine solution providing) artificial flowers with two different polarization patterns. However, the bees could only discriminate between the two targets when the targets were viewed from below.
Polarization patterns occur on the petals of real flowers, but are invisible to humans and thus may be a hitherto overlooked component of floral signalling. Around 53 percent of flower species face downwards, so their polarization patterns are presented in such a way as to be visually accessible to the region of the bee’s eye, which includes the polarization sensitive Dorsal Rim Area. Light reflected from downward facing flowers also has the potential to contrast with skylight polarization patterns, potentially helping the bee to detect and identify such flowers.
“Both pollinator and plant fitness is greatly dependent on the ability of pollinators to discriminate flowers accurately,” Professor Partridge said. “Bees have been shown to be able to use a wide range of floral cues, including color, shape, texture, certain chemical compounds and temperature, to improve the identification and recognition of flowers.”
“Recent findings have added floral humidity and electric fields as additional methods with which pollinators can discriminate flowers, and it is advantageous for a plant to produce a number of different signals that a pollinator can utilize effectively,” he continued. “Our findings suggest polarization vision may provide sensory access to an additional floral cue for bees.”
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